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4G Mobile Communications

Explore the history of 4G mobile communications, including the IMT-Advanced specification and the development of technologies such as Mobile WiMAX and LTE. Discover the challenges faced in terms of coverage, capacity, and spectrum, and learn about the features of WiMAX, including OFDM, adaptive modulation and coding, and error correction techniques.

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4G Mobile Communications

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  1. 4G Mobile Communications www.assignmentpoint.com

  2. History • In March 2008, the International Telecommunications Union-Radio (ITU-R) specified a set of requirements for 4G standards, named the International Mobile Telecommunications Advanced (IMT-Advanced) specification, setting peak speed requirements for 4G service at 300 Mbit/s for high mobility communication (such as from trains and cars) and 1Gbit/s for low mobility communication (such as pedestrians and stationary users). • Since the first-release versions of Mobile WiMAX (first used in South Korea in 2007) and LTE (in Oslo, Norway and Stockholm, Sweden since 2009 ) support much less than 1 Gbit/s peak bit rate, they are not fully IMT-Advanced compliant, but are often branded 4G by service providers. • On December 6, 2010, ITU-R recognized that these two technologies, as well as other beyond-3G technologies that do not fulfill the IMT-Advanced requirements, could nevertheless be considered "4G", provided they represent forerunners to IMT-Advanced compliant versions . www.assignmentpoint.com

  3. During the spring 2011 above two system provide their advanced version as: Mobile WiMAX Release 2 (also known as WirelessMAN-Advanced or IEEE 802.16m) and LTE Advanced (LTE-A, Based on UMTS 3G technology) and promising speeds in the order of 1 Gbit/s in 2013. www.assignmentpoint.com

  4. Comparison of 3G and 4G www.assignmentpoint.com

  5. Some Key Challenges Coverage Transmit power limitations and higher frequencies limit the achievable cell size Capacity Current air interfaces have limited peak data rate, capacity, and packet data capability Spectrum Lower carrier frequencies (< 5 GHz) are best for wide-area coverage and mobility www.assignmentpoint.com

  6. WiMAX Wi-MAX: The Worldwide Interoperability for Microwave Access, is a technology aimed at providing wireless data over long distances It is based on the IEEE 802.16 standard. Fig.1 www.assignmentpoint.com

  7. WiMAX • In 1998 IEEE802.16 protocol was developed to provide high speed service of WMAN (Wireless Metropolitan Area Network). Next two new version of above protocol were found as: IEEE 802.16d (in 2004) was developed to support high speed wireless data service of fixed user and its later version IEEE 802.16e (in 2005) supports both fixed and mobile users. • With the advent of OFDMA based IEEE 802.16e, research is now going on to implement VoIP service with adaptive modulation and channel coding (MCS) scheme. To enhance the throughput of the wireless system the modulation and coding scheme of the transmitter is changed according to the fading condition of the channel. • Therefore the service becomes a variable bit rate service where the bit rate depends on the fading condition of the wireless channel. www.assignmentpoint.com

  8. Three common types of BW allocation algorithms are:Dedicated Resource Allocation (Unsolicited Grand Service known as UGS Algorithm) where fixed amount of BW is allocated to each user hence possibility of waste of BW when a user needs to data send data at low rate; Polling-Based Resource Allocation (Real-Time Polling Service called rtPS Algorithm) where BS allocates the BW dynamically therefore incurs some protocol overhead and delay; Hybrid Resource Allocation Algorithm is the combination of above two. • WiMAX also can be used as a complementary system to Wi-Fi. Both of the two major 3G systems: CDMA2000 and UMTS, compete with WiMAX. www.assignmentpoint.com

  9. WiBro, Korean version of WiMAX has been deployed in Korea. • WiFi and WiMAX are the B3G (Beyond 3G) systems. WiMAX may be an interim system of a 4G system. www.assignmentpoint.com

  10. Some important features of WiMAX are given below: OFDM in physical layer: The access technique used in physical layer of WiMAX is OFDM; where the high speed serial data is converted to low rate parallel streams and each stream is modulated by separate carrier each one is known as subcarrier. Subcarriers are mutually orthogonal and deals with low data rate hence can protect multipath fading. Very high peak data rates: The data rate of WMAX is 70Mbps under the channel of bandwidth of 20 MHz. The rate can be further increased using space division multiplexing i.e. incorporation of multiple antennas. www.assignmentpoint.com

  11. Adaptive Modulation and Coding: The IEEE 802.16e standard changes modulation and channel coding scheme based on received SNR. For example a SS close to the BS can use a high modulation scheme (more bits per symbol) i.e. the system can get more capacity but when the SS is at the cell boarder the system permits lower modulation scheme (increased signal space on orthogonal basis function coordinate system) to avoid huge symbol error rate. Therefore the system can overcome the time selective fading (the channel condition is better at some instant than other). Error Correction Techniques: WiMAX incorporates two types of strong error correction techniques: FEC (Forward Error Correction) for multimedia traffic and ARQ (Automatic Repeat Request) for data traffic to improve throughput.  www.assignmentpoint.com

  12. Support for TDD and FDD: Like mobile cellular communication it supports both FDD (Frequency division duplexing) and TDD (Time division duplexing), as well as a half-duplex FDD. Above features provide the flexibility of using same or different carriers for up and down link. Time Division Duplexing Time division duplexing (TDD) refers to the interleaving of transmission and reception of data on the same frequency. A common frequency is shared between the upstream and downstream, the direction in transmission being switched in time. Frequency Division Duplexing Frequency division duplexing (FDD) refers to the simultaneous transmission and reception of data over separate frequencies, allowing for bidirectional full-duplex communications. www.assignmentpoint.com

  13. Fig.2 IEEE 802.16 general architecture www.assignmentpoint.com

  14. OFDMA Based WiMAX Network We consider a single cell in a WiMAX network with a base station and multiple subscriber stations (Fig.3). Each subscriber station serves multiple connections. Admission control is used at each subscriber station to limit the number of ongoing connections through that subscriber station. At each subscriber station, traffic from all users for uplink connections are aggregated into a single queue. www.assignmentpoint.com

  15. Fig.3 System model The size of this queue is finite (i.e., X packets) in which some packets will be dropped if the queue is full upon their arrivals. The OFDMA transmitter at the subscriber station receives packets and transmits them to the base station. The base station may allocate different number of subchannels to different subscriber stations. For example, a subscriber station with higher priority could be allocated more number of subchannels. www.assignmentpoint.com

  16. IEEE 802 Activities • Wired • 802.3: Ethernet • 802.17: Packet Ring (new) • Wireless • 802.11: Wireless LAN • Local Area Network • 802.15: Wireless PAN • Personal Area Network (e.g. BluetoothTM) • 802.16: WirelessMANTM • Metropolitan Area Networks www.assignmentpoint.com

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  18. 1. What is 4G? Wireless Technology Evolution to 3.9G CDMA IEEE Cellular IEEE LAN GSM/UMTS CDMA (IS-95A) GSM TDMA IS-136 IEEE 802.16 IEEE 802.11 2G CDMA (IS-95B) GPRS 802.11g 2.5G cdma 2000 E-GPRS EDGE WCDMA FDD/TDD TD-SCDMA LCR-TDD 802.11a 3G 1xEV-DO Rev 0/A/B HSDPA FDD/TDD HSUPA FDD/TDD Fixed WiMAX 802.16d WiBRO 802.11g 3.5G UMB 802.20 HSPA+ Mobile WiMAX 802.16e 802.11n LTE E-UTRA 3.9G www.assignmentpoint.com Fig.4

  19. In a hierarchical telecommunications network the backhaul portion of the network comprises the intermediate links between the core network or backbone, of the network and the small sub-networks at the "edge" of the entire hierarchical network. www.assignmentpoint.com

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  22. Wi-Fi • Wi-Fi, which stands for “wireless fidelity,” is a radio technology that networks computers so they connect to each other and to the Internet without wires. Users can share documents and projects, as well as an Internet connection, among various computer stations and easily connect to a broadband Internet connection while traveling. By using a Wi-Fi network, individuals can network desktop computers, laptops, and PDAs and share networked peripherals such as servers and printers. www.assignmentpoint.com

  23. A Wi-Fi network operates just like a wired network, but without the restrictions imposed by wires. It uses radio technologies called IEEE 802.11a, 802.11b, or 802.11g to provide secure, reliable, fast wireless connectivity. A Wi-Fi network can be used to connect computers to each other, to the Internet, and to wired networks (which use IEEE 802.3 or Ethernet). Wi-Fi networks operate in the unlicensed 2.4-and 5-GHz radio bands with an 11-Mbps (802.11b) or 54-Mbps (802.11a) data rate, or with products that contain both bands (dual band). www.assignmentpoint.com

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  25. Upper layers Service specific convergence layer MAC sub-layer Security sub-layer Transmission convergence sub-layer QPSK 16-QAM 64-QAM Layers of WiMAX Data link layer Physical layer Security Sublayer provides authentication, secure key exchange and encryption between SS and BS. Fig.5 The 802.16 protocol stack www.assignmentpoint.com

  26. 802.16 PHY • Burst Uplink (A data burst (PDU) in a downlink or in an uplink consists of several slots). • Downlink • Mode A: continuous transmission stream supporting concatenation of Reed Solomon coding, interleaving, and convolutional coding for use in an FDD only system • Mode B: burst format supporting FDD with adaptive modulation as well as TDD and half-duplex FDD • Modulation • QPSK, 16-QAM, 64-QAM www.assignmentpoint.com Fig.6

  27. Adaptive Modulation and Coding • An SS (subscriber Station) close to the BS could use a high modulation scheme, thereby giving the system more capacity. In contrast, a weak signal from a more remote subscriber might only permit the use of a lower modulation scheme to maintain the connection quality and link stability. • This feature enables the system to overcome time-selective fading. • The coding rate also change according received SNR of fading channel. www.assignmentpoint.com

  28. Modulation Coding Schemes (MCSs) PDU → Packet Data Unit SDU → Service Data Unit lm → the number of TDMA slots /PDU www.assignmentpoint.com

  29. Uplink scheduling is feasible if the allocated uplink resources are less than the total of available resources (number of PDU/slot) Nslot,u. Hence, we have where the parameter lm is the size of the VoIP PDU, which is modulated with the mth MCS level after encoding and xm is the number of PDU at mth MCS level. www.assignmentpoint.com

  30. For example, we consider Nslot,u = 50 and M = 4. Then,the MCS-level distributions of packets are denoted as, X =(x1, x2, x3, x4). If the MCS-level distributions of six packets in the uplink queue are (0, 0, 0, 6) or (0, 0, 1, 5) and the MCS level of the seventh packet in the queue is not four, the BS schedules six packets according to the uplink feasibility condition. X = (0, 0, 0, 6) = 0 + 0 + 0 + 6*6 = 36 <50 X = (0, 0, 1, 5) = 0 + 0 + 1*12 + 5*6 = 42 < 50 www.assignmentpoint.com

  31. However, if the MCS level of the seventh packet is four, the BS can schedule more packets than six because the MCS-level distribution of seven packets becomes (0, 0, 0, 7) or (0, 0, 1, 6), which satisfies feasibility condition. X = (0, 0, 0, 7) = 0 + 0 + 0 + 6*7= 42 <50 X = (0, 0, 1, 6) = 0 + 0 + 1*12 + 6*6= 48 <50 www.assignmentpoint.com

  32. Upper layers Service specific convergence layer MAC sub-layer Security sub-layer Transmission convergence sub-layer QPSK 16-QAM 64-QAM Transmission convergence sub-layer (TCS) converts MAC PDUs of variable size into proper-length (fixed size) FEC (Forward Error Correction) blocks. www.assignmentpoint.com

  33. Upper layers Service specific convergence layer MAC sub-layer Security sub-layer Transmission convergence sub-layer QPSK 16-QAM 64-QAM Data link layer From the reference model as illustrated in Figure 7, there are three sub-layers in the data link layer composed of i) a security sublayer, ii) a MAC common part sublayer, and iii) a convergence sublayer. It provides only connection oriented service Fig.7 The 802.16 protocol stack www.assignmentpoint.com

  34. Service Specific Convergence Sub-layer (CS): • The CS, which is the interface between the MAC layer and layer 3 of the network, receives data packets from the higher layer. These higher layer packets are known as service data unit (SDU). • The CS is responsible for performing all operations that are dependent on the nature of higher-layer protocol (ATM, IPv4, IPv6 etc), such a header compression and address mapping. The CS can be viewed as an adaptation layer that masks the higher-layer protocol. www.assignmentpoint.com

  35. Packet header suppression (PHS): At the transmitter it involves removing the repetitive part of the header of each SDU. For example, if the SDUs delivered to the CS are IP packets, the source and destination addresses contained in the header of each IP packet do not change from one packet to the next and thus can be removed before being transmitted over the air. Similarly at the receiver: the repetitive part of the header can be reinserted into the SDU before being delivered to the higher layer. • CS is also responsible for the mapping the higher layer address, such as IP address, of the SDUs into the identity of the PHY and MAC connections to be used for its transmission. The WiMAX MAC layer is connection oriented and identifies a logical connection between the BS and the MS by a unidirectional connection identifier (CID). The CID for UP and DL connections are different. www.assignmentpoint.com

  36. MAC Common Part Sublayer • The MAC layer takes packets from the upper layer (CS) and these packets are called MAC service data units (MSDUs) and organize them into MAC protocol data units (MPDUs) for transmission over the air. • The WiMAX MAC uses a variable length MPDU and offer a lot of flexibility to allow for their efficient transmission. For example multiple MPDUs of same or different lengths may be arranged into a single burst when they are destined to the same receiver. www.assignmentpoint.com

  37. Similarly , multiple MSDUs from the same higher-layer service may be concatenated into a single MPDU to save MAC header overhead. • Large MSDUs may be fragmented into smaller MPDUs and send across multiple frames. When an SDU is fragmented, the position of each fragment within the SDU is tagged by a sequence number. The sequence number enables the MAC layer at the receiver to assemble the SDU from its fragments in the correct order. • WiMAX has two types of PDUs, each with a very different header structure. • The generic MAC PDU is used for carrying data and MAC-layer signaling messages. • The bandwidth request PDU is used by the MS to indicate to the BS that more BW is required in UL, due to pending data transmission. A bandwidth request PDU consists only of a bandwidth-request header, with no payload or CRC. www.assignmentpoint.com

  38. Each MAC frame is prefixed is prefixed with GMH (generic MAC header). • Field (in SH) to indicate whether the payload is encrypted or not. If the payload is encrypted then the encryption key is also given. • Header CRC field is a checksum over the header only using the generator polynomial x8+x2+x+1. The length of this field is 8bits. GMH Other SH Packed fixed size MSDU Packed fixed size MSDU CRC ……. Fig.6 MAC PDU frame carrying several-fixed length MSDUs packed together GMH → Generic MAC Header (used for carrying data and MAC-layer signaling messages) SH → Sub-header www.assignmentpoint.com

  39. LEN H E rs C EKS rs msb Type (6 bits) T C v I (2) v (3) CID msb (8) LEN lsb (8) HCS (8) CID lsb (8) Generic MAC Header Fields www.assignmentpoint.com

  40. BW Req. H E Type (3 bits) T C msb (11) CID msb (8) BWS Req. lsb (8) HCS (8) CID lsb (8) Bandwidth Request MAC Header Fields www.assignmentpoint.com

  41. GMH Other SH FSH MSDU Fragment CRC GMH Other SH PSH Variable size MSDU or Fragment PSH Variable size MSDU or Fragment CRC … Fig.8 MAC PDU frame carrying a single fragmented MSDU Fig.9 MAC PDU frame carrying several variable length MSDUs packed together FSH → Fragmentation Sub-header PSH → Packing Sub-header The type of payload is identified by the sub-header immediately precedes it. For example FSH or PSH of above figure. www.assignmentpoint.com

  42. Generic MAC Header Format BW Req. Header Format (Header Type (HT) = 0) (Header Type (HT) =1) LEN BW Req. H E rs C EKS rs H E msb Type (6 bits) Type (6 bits) T C v I (2) v T C msb (8) (3) CID msb (8) LEN lsb (8) CID msb (8) BWS Req. lsb (8) HCS (8) CID lsb (8) HCS (8) CID lsb (8) msb lsb Generic MAC CRC payload (optional) Header MAC PDU (optional) (6 bytes) www.assignmentpoint.com

  43. Privacy (or Security) Sub-layer: supporting authentication, secure key exchange, and encryption. www.assignmentpoint.com

  44. Evolution of LTE 1G 2G 2.5G 3G 4G www.assignmentpoint.com

  45. Comparison of LTE Speed www.assignmentpoint.com

  46. The LTE- Advanced (Long Term Evolution- Advanced) is 4G wireless service proposed by 3GPP (Third generation Partnership Project). In 2009 4G LTE started its commercial service in Scandinavia. Two important features of LTE are: femtocell deployment and OFDMA-based physical layer access. The architecture of LTE consists of two major parts: the E-UTRAN (Evolved Universal Terrestrial Radio Access Network) and the EPC (Evolved Packet Core). The first part provides air interface between MS or UE to BS and the second part is interconnected switching network called backbone or core network. www.assignmentpoint.com

  47. The EPC consists of six nodes: Home Subscriber Server (HSS) is like the combination of HLR and AUC of UMTS or GSM  The Packet Data Network (PDN) Gateway (P-GW) provides connectivity between UE and external packer switching network. It works like a gateway SGSN of UMTS. The serving gateway (S-GW) works as a router whose function is to forward data between the BS and the PDN gateway. It also works as the mobility anchor of eNB handovers and do the similar job between LTE and other 3GPP technologies. www.assignmentpoint.com

  48. The MME (for Mobility Management Entity) deals with the signaling (between UE and CR) related to mobility of users, paging of UE in idle-mode and security for E-UTRAN access. The Policy Control and Charging Rules Function (PCRF): This module works like: Packet filtering and billing on flow basis.  ePDG (Evolved Packet Data Gateway) provides secured data transmission between UE to EPC over an untrusted non-3GPP access. www.assignmentpoint.com

  49. S-GW HSS Macro Femto E-UTRAN ePDG P-GW Untrusted non 3GPP access Trusted non 3GPP access Fig.10 Architecture of LTE www.assignmentpoint.com

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